Forelimb-Hindlimb Developmental Timing Changes across Tetrapod Phylogeny The Harvard community has made this article openly available. Please share how this access benefits you. Your story matters Citation Bininda-Emonds, Olaf R.P., Jonathan E. Jeffery, Marcelo R. Sánchez- Villagra, James Hanken, Matthew Colbert, Claude Pieau, Lynne Selwood, et al. 2007. Forelimb-hindlimb developmental timing changes across tetrapod phylogeny. BMC Evolutionary Biology 7:182. Published Version doi:10.1186/1471-2148-7-182 Citable link http://nrs.harvard.edu/urn-3:HUL.InstRepos:4461122 Terms of Use This article was downloaded from Harvard University’s DASH repository, and is made available under the terms and conditions applicable to Other Posted Material, as set forth at http:// nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of- use#LAA BMC Evolutionary Biology BioMed Central Research article Open Access Forelimb-hindlimb developmental timing changes across tetrapod phylogeny Olaf RP Bininda-Emonds†1,2, Jonathan E Jeffery†1, Marcelo R Sánchez- Villagra†3, James Hanken4, Matthew Colbert5, Claude Pieau6, Lynne Selwood7, Carel ten Cate1, Albert Raynaud8, Casmile K Osabutey9 and Michael K Richardson*1 Address: 1Institute of Biology, University of Leiden, Kaiserstraat 63, 2311GP, Leiden, The Netherlands, 2Institut für Spezielle Zoologie und Evolutionsbiologie mit Phyletischem Museum, Friedrich-Schiller-Universität Jena, Erbertstrasse 1, 07743 Jena, Germany, 3Palaeontologisches Institut und Museum, Karl Schmid-Strasse 4, CH-8006 Zürich, Switzerland, 4Museum of Comparative Zoology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA, 5Department of Geological Sciences, The University of Texas, Austin, TX 78712, USA, 6Laboratoire de Biochimie du Développement, Institut Jacques Monod, CNRS et Université Paris 6 et 7, Tour 43-33, E3, 2, place Jussieu, 75251 Paris Cedex 05, France, 7Department of Zoology, Gate 12, University of Melbourne, Victoria. 3010, Australia, 8Formerly of Laboratoire Pasteur (Embryologie expérimentale), 20 rue des Moulins, 95110 Sannois, France and 9Department of Anatomy, St George's Hospital Medical School, Tooting, London SW17 0RE, UK Email: Olaf RP Bininda-Emonds - [email protected]; Jonathan E Jeffery - [email protected]; Marcelo R Sánchez- Villagra - [email protected]; James Hanken - [email protected]; Matthew Colbert - [email protected]; Claude Pieau - [email protected]; Lynne Selwood - [email protected]; Carel ten Cate - [email protected]; Casmile K Osabutey - [email protected]; Michael K Richardson* - [email protected] * Corresponding author †Equal contributors Published: 1 October 2007 Received: 26 February 2007 Accepted: 1 October 2007 BMC Evolutionary Biology 2007, 7:182 doi:10.1186/1471-2148-7-182 This article is available from: http://www.biomedcentral.com/1471-2148/7/182 © 2007 Bininda-Emonds et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Background: Tetrapods exhibit great diversity in limb structures among species and also between forelimbs and hindlimbs within species, diversity which frequently correlates with locomotor modes and life history. We aim to examine the potential relation of changes in developmental timing (heterochrony) to the origin of limb morphological diversity in an explicit comparative and quantitative framework. In particular, we studied the relative time sequence of development of the forelimbs versus the hindlimbs in 138 embryos of 14 tetrapod species spanning a diverse taxonomic, ecomorphological and life-history breadth. Whole-mounts and histological sections were used to code the appearance of 10 developmental events comprising landmarks of development from the early bud stage to late chondrogenesis in the forelimb and the corresponding serial homologues in the hindlimb. Results: An overall pattern of change across tetrapods can be discerned and appears to be relatively clade-specific. In the primitive condition, as seen in Chondrichthyes and Osteichthyes, the forelimb/pectoral fin develops earlier than the hindlimb/pelvic fin. This pattern is either retained or re-evolved in eulipotyphlan insectivores (= shrews, moles, hedgehogs, and solenodons) and taken to its extreme in marsupials. Although exceptions are known, the two anurans we examined reversed the pattern and displayed a significant advance in hindlimb development. All other species examined, including a bat with its greatly enlarged forelimbs modified as wings in the adult, showed near synchrony in the development of the fore and hindlimbs. Page 1 of 7 (page number not for citation purposes) BMC Evolutionary Biology 2007, 7:182 http://www.biomedcentral.com/1471-2148/7/182 Conclusion: Major heterochronic changes in early limb development and chondrogenesis were absent within major clades except Lissamphibia, and their presence across vertebrate phylogeny are not easily correlated with adaptive phenomena related to morphological differences in the adult fore- and hindlimbs. The apparently conservative nature of this trait means that changes in chondrogenetic patterns may serve as useful phylogenetic characters at higher taxonomic levels in tetrapods. Our results highlight the more important role generally played by allometric heterochrony in this instance to shape adult morphology. Background A largely unanswered question is how these differences What evolutionary mechanisms are responsible for differ- are reflected in the ontogenetic development of the limbs. ences in the relative size of body parts among organisms? Limbs are one of the best studied systems in both evolu- This basic question has long been confronted by biolo- tion and development [3] and display a sequence of well- gists, for example, by J. S. Huxley, in his Problems of Rela- defined temporal events, such as formation of the apical tive Growth [1]. When considering the tetrapod limb, one ectodermal ridge (AER) and the chondrification of skele- might ask why the forelimbs are relatively larger or tal elements. We examine here the extent to which fea- smaller than the hindlimbs in some species, and how tures of early limb development, especially these differences have arisen during evolution. chondrogenesis, might be associated with obvious differ- ences in forelimb and hindlimb size or function in the Tetrapods exhibit great diversity in limb structures among adult. We concentrate on heterochrony, the evolutionary species and in differences between fore- and hindlimbs change in developmental timing, a process which is within species, which typically are correlated with loco- thought to be important and common in evolution [4]. In motor modes and life history [2]. Among mammals, the particular, we examine the relative timing of developmen- relatively large wings of an adult bat exhibit a striking con- tal events during ontogeny across the phylogeny of the trast in size and proportions to its legs, whereas the dispar- species examined (sequence heterochrony; sensu [5]). ity in most other living eutherians (e.g. mice) is more modest. Kangaroos represent the opposite situation, hav- Results ing relatively massive hindlimbs. These differences are not The average event-pair score (EPS; see Methods) was plot- restricted to mammals but characterize tetrapods as a ted for each species (Table 1, Fig. 1). The two anurans whole, as evidenced when considering a bird or a frog or (Xenopus, Eleutherodactylus) show average EPS scores sig- a turtle, or fossils such as Tyranosaurus rex, which has huge nificantly less than one, indicating that hindlimb devel- hindlimbs and tiny forelimbs. opment generally precedes that of the forelimb (noted by [6,7]). The two birds (Taeniopygia, Gallus) also tend to Table 1: Statistics on the temporal distribution of developmental events Species (common name) N Avg. Stage EPS Student's t Eleutherodactylus coqui (tree frog) 12 3.091 0.656 ± 0.110 t63 = -3.136 (P = 0.0026) Xenopus laevis (clawed toad) 6 4.860 0.625 ± 0.108 t63 = -3.473 (P = 0.0009) Emys orbicularis (pond turtle) 10 3.333 1.020 ± 0.093 t99 = 0.215 (P = 0.8305) Lacerta viridis (wall lizard) 12 2.857 1.020 ± 0.093 t99 = 0.215 (P = 0.8305) Gallus gallus (chicken) 10 2.188 0.875 ± 0.121 t63 = -1.033 (P = 0.3054) Taeniopygia guttata (zebra finch) 7 3.091 0.922 ± 0.112 t63 = -0.697 (P = 0.4882) Trichosurus vulpecula (brushtail possum) 15 2.500 1.640 ± 0.076 t99 = 8.432 (P < 0.0001) Sminthopsis macroura (stripe-faced dunnart) 5 8.000 1.730 ± 0.060 t99 = 12.155 (P < 0.0001) Dasyurus viverrinus (marsupial cat) 11 3.077 1.850 ± 0.048 t99 = 17.732 (P < 0.0001) Erinaceus europaeus (hedgehog) 10 3.333 1.200 ± 0.094 t99 = 2.121 (P = 0.0364) Talpa europea (mole) 10 3.333 1.230 ± 0.089 t99 = 2.596 (P = 0.0109) Mus musculus (mouse) 12 2.857 1.090 ± 0.096 t99 = 0.933 (P = 0.3533) Rousettus amplexicaudatus (fruitbat) 10 3.800 1.000 ± 0.101 t89 = 0.000 (P = 1.000) Cynocephalus variegatus (flying lemur) 8 3.333 1.080 ± 0.088 t99 = 0.905 (P = 0.3677) The event-pair score (EPS; presented as average ± SE) may range from 2 (forelimb advanced over hindlimb) to 0 (hindlimb advanced over forelimb). Two-tailed Student's t-tests were used to determine if the EPS was significantly different from 1. N is the number of stages of limb development identified and Avg. Stage is the mean number of events that occurred at each stage. Page 2 of 7 (page number not for citation purposes) BMC Evolutionary Biology 2007, 7:182 http://www.biomedcentral.com/1471-2148/7/182 *DOOXV (P\V 0XV 'DV\XUXV 2. diapsids (lizards, turtles, and birds): slight, but insignif- icant hindlimb acceleration with an average EPS of 0.973 ± 0.051; &, 3. eutherian mammals: slight, but insignificant forelimb acceleration with an average EPS of 1.122 ± 0.042; 4.